1. Field
The following description generally relates to a technology for passive optical communication, and more particularly to a passive optical network apparatus using mode-division multiplexing.
2. Description of the Related Art
A Passive Optical Network (PON) apparatus is composed of an optical line terminal (OLT) of a communication service provider side, an optical network unit (ONU) of a subscriber side, and optical cables and an optical distribution network that connect the OLT and the ONU.
In the Time Division Multiplexing (TDM), which is a multiplexing method used by a passive optical network apparatus, a downstream optical signal, output from an OLT, is split by a passive optical splitter and is transmitted to a plurality of ONUs, while upstream optical signals, output from a plurality of ONUs, are transmitted to the OLT through the passive optical splitter.
However, in the TDM-PON, loss occurs in the optical power splitter and the loss in the optical power splitter increases with a splitting ratio. For example, in the case where an optical signal is split into four branches, a splitting loss of 6 dB or more occurs, and in the case where an optical signal is split into 32 branches, a splitting loss of 15 dB or more occurs. Such loss in the optical power splitter causes many losses, such as a loss of a Feeder line and a loss in a power budget of an OLT/ONU. For this reason, there is a difficulty in increasing the number of subscribers and the length of a Feeder line. Korean Laid-open Patent Publication No. 10-2009-0100083 discloses a passive optical network system, and a method of increasing a signal transmission distance and branching ratio. However, a separate reproducing unit is required in the system.